1. Field of the Invention
The present invention relates to fire suppression systems, and, more particularly, to a fire suppression system for chemical process stations.
2. Description of the Related Art
Many applications require fabrication of devices in controlled environments that provide little or no contamination, and these controlled environments are commonly referred to as "clean rooms". Fabrication of semiconductor devices, for example, as highly integrated circuits, is typically a multi-step, chemical process performed in process stations of a clean room. Process stations, also known as, for example, wet benches, chemical wet stations, and chemical process stations, are typically constructed of materials such as polypropylene, fire-retardant polypropylene, poly-vinyl chloride (PVC) or stainless steel. Further, the process stations usually contain volatile chemicals and gases, or heated baths of corrosive chemicals, which may easily ignite, causing a fire hazard. Since many process stations may be constructed of materials that may burn, such as polypropylene or PVC, the fire hazard extends to combustion of the process station itself.
Consequently, process stations typically include a fire detection and suppression system that is coupled to plant facilities. Some process stations simply employ a sprinkler head similar to those commonly used in the sprinkler system of the plant. Some systems include more advanced fire suppression techniques. Process stations may include a fire detector that may be a heat sensor or an infrared (IR) or ultra-violet (UV) based electro-optical fire detector. These fire detectors may have an ability to detect, for example, a heat-release rate of 13-kilowatts (kW) corresponding to an 8-inch diameter polypropylene pool fire. The fire detector signals an electrically operated valve, such as a solenoid valve, to provide a fire suppressant through a nozzle to the interior of the process station to extinguish the fire.
The fire suppressant, which may be a gas or liquid, is usually distributed to the process station by a dedicated system for that station, or distributed through the plant to all process stations through a dedicated distribution (piping) system. Some spray systems employ high-pressure foam added to the liquid for added performance. Such fire suppressants and related distribution systems are costly both to install and maintain. These systems, and existing sprinkler-based systems installed in process stations, tend to provide a high volumetric flow rate of the fire suppressant, causing widespread contamination of the clean room. Alternatively, to reduce contamination, some fine-spray systems employ a gas, such as air, nitrogen or carbon dioxide, injected into the nozzle with the liquid to provide accelerated delivery and atomizing of the liquid.